Monday, December 14, 2009

Goalie and Faceoffs

Some of the most interesting new statistics introduced by stats guys in the blogosphere have been numbers that track how many defensive and offensive zone faceoffs players are put on the ice for. For skaters, this helps adjust for the way they are being used by their coach, since for example it is an advantage for an offensive player to start their shift in the other team's end rather than having to move the puck 180 feet down the ice to get it into a scoring position. Faceoff numbers can also be used to measure which players are driving possession, by seeing whether a player ends their shift more often in the offensive or defensive zone.

I haven't seen anyone apply these numbers yet to goalies. Since goalies don't change lines, the starting and ending shift numbers are of course meaningless. However, on many shots goalies have the opportunity to either freeze or play the puck, and that choice affects the number of defensive zone draws their teams face. Also, if certain goalies are able to contribute to their teams in other ways, such as for example through their puckhandling skills, then it might show up by their team taking more draws at the other end of the rink.

Vic Ferrari at timeonice has the faceoff zone start numbers for every player in the league last year, including goalies. I'll stick to the convention used by Gabe Desjardins at Behind the Net where he has the offensive faceoff percentage for all players, a number calculated by ignoring the neutral zone faceoffs and dividing the number of offensive zone faceoffs by the total number of draws in offensive and defensive zone combined.

The correlation between the offensive faceoff percentage for starters and their backups was 0.51, which suggests that the rest of the team has a big impact on puck possession and faceoffs. That should be fairly uncontroversial. I'd expect with a bigger sample size for most of the backup goalies that number would be higher.

The correlation between offensive faceoff percentage and shots faced per 60 minutes was -0.57. I was expecting that relationship to be stronger, since all the Corsi evidence shows a big advantage to starting in the other team's zone, but again EV only for one season is a fairly small sample so there is likely a reasonable degree of luck in the numbers.

There were 9 teams that had a offensive faceoff percentage difference of 5% or more between their starting goalie and his backups. Here are the faceoff numbers for each of those teams, along with the offensive faceoff percentages and shots faced per 60 minutes:

The Price/Halak gap is interesting and appears to account for some of the shot differential between them, but I'm not sure how much it had to do with the goalies. I'd bet the split would be in the other direction if we were looking at this season's numbers, based on how Montreal has played in front of each of them in 2009-10. Most of the others either involve backups who didn't play very much or goalies who I wouldn't expect to have much of an effect on faceoffs, although there is one notable exception.

The biggest gap between any starter and backup, by far, is in New Jersey. Knowing what we know about those goalies, I'd say that these numbers suggest a real effect. In most starter/backup scenarios, we have to at least consider the possibility of strength of schedule being a factor, but that wasn't the case here as Clemmensen was an injury replacement for Brodeur. The Devils weren't performing exactly the same all the way through the season, but all three of their goalies had similar GAAs so it is likely that they played in fairly similar environments.

The numbers indicate that Brodeur is either helping shift the play to the other end of the ice or freezing the puck less often than the other goalies. Here are the faceoff numbers for New Jersey's goalies broken down per 60 minutes of EV play:

Brodeur keeps the puck moving a lot more than the other two (and indeed, he probably keeps it moving more than any other goalie in the league). However, the team did not take substantially more faceoffs at the other end of the rink, which makes it uncertain whether Brodeur's impact translates to the offensive side of the rink (although I would certainly like to see more data on this one).

Consistently giving the puck to teammates instead of allowing the opposing team to win control of it through a faceoff should help a team, and this may account for some of the observed shot differentials between Brodeur and his backup goalies. There are other possible benefits, such as creating more changes on the fly, which could be to the benefit of a smart bench coach who wants to get his matchups. I'd expect some tradeoff in terms of increased turnovers, but Brodeur is likely pretty efficient.

I think these results also shed a bit more light on the rebound numbers discussed earlier here that showed Clemmensen allowing a lower rate of rebound shots against than Brodeur. Given that Brodeur would have been playing the puck much more often and attempting to direct his rebounds rather than simply freezing the puck, that means he would have been facing many more opportunities to turn over the puck or for the other team to steal it and get a quick shot on goal. If Brodeur was aggressive in terms of directing rebounds and playing the puck while Clemmensen was conservative (and probably helped by a defence that gave extra attention to clearing the crease), then that would explain why Brodeur's numbers don't seem as good despite his superior skill. More opportunities usually mean more errors, no matter how good you are.

This is just a cursory look from one year's worth of data, but looking at a few more seasons' worth of data could help us better identify Brodeur's effect here and see whether any other goalies seem to have a tendency towards freezing or moving the puck.

Good stuff, CG. We had a bit of a discussion along these lines over at the Copper & Blue during the EDM @ DAL game day thread a while back. Scott noticed that every Dallas player had a Zone Start number of > 50% offensive zone, and my immediate response was "Turco". While hardly scientific, we did watch the tendencies of the two goalies throughout that game and it was apparent that Deslauriers would freeze the puck at almost every opportunity while Turco would move it if he possibly could. Surely that will affect team faceoffs in a major way over time. There may also be a relationship to Shots Against although there are bound to be competing factors.

One caveat: the data you cite at TimeOnIce seems to be incomplete. There was a crash on that site last year, and when the faceoff data was restored in the post you cite, all the numbers were considerably lower. See my comments right under that post which unfortunately Vic doesn't seem to have read (I didn't come across this article until 3 weeks after it was written). Also compare this example to this one. Same thing happened on a few other random tests; TimeOnIce gross numbers seem to be around 60% of BehindTheNet that the data is incomplete rather than corrupted; my best guess is that the data got cut off around the All-Star break. (I was tracking the Oilers all year, and remember noting that 226/114 ratio for Brodziak at one point, a 2:1 ratio which moderated somewhat down the stretch; also Horcoff's ZoneStarts got even more difficult down the stretch which is consistent with this assumption.) It's also possible that the "new" data was Start of Shift faceoffs rather than all faceoffs, which has no relevance w.r.t. goaltenders. Too bad, because TimeOnIce has goalie data and BehindTheNet doesn't.

So Brodeur's stats, while very impressive indeed, are likely only from those games before he got hurt rather than the full sample. Note too how this will skew your "faceoffs per 60" right across the board. In retrospect, those numbers posed don't pass the smell test because they are simply too low; Brodeur, Clemmensen and Weekes are all in the 20-30 O + D Zone faceoffs per 60, and even adjusting for neutral zone faceoffs would take us nowhere near the expected ~1 faceoff per minute.

Bruce: I wasn't aware of the data issue, thanks for pointing that out. I am not too familiar with these numbers so I didn't know what the baseline was, but if we should be expecting 1 faceoff per minute then certainly the numbers are low.

I think these must be shift start faceoffs only, because as I recall Vic had a different script that he used to generate the end of shift faceoff numbers which gave each player's ZoneShift.

So yeah, that's really the wrong sample to look at for goalies, and the per 60 numbers won't mean much.

Re: Turco, for what it's worth his offensive faceoff percentage last year was 49% according to Time on Ice. His backups played so little that they don't really give us a good basis for comparison, but they combined for 52%.

I didn't know what the baseline was, but if we should be expecting 1 faceoff per minute then certainly the numbers are low.

CG: Just a rule of thumb that I have used post-lockout but it seems to be on the money.

Hitting up faceoff stats on NHL.com, in 2009-10 the Oilers have taken 1785 faceoffs in 32 games plus 8 OT periods, about 56 faceoffs per game. Of these ~43 are at EV, 7 on PP and 6 on PK.

Tonight's opponents the Kings have taken 1904 faceoffs in 35 games, almost 60 per game, about 45 at EV and the other 15 split between the special teams.

Brodeur's Devils have taken 1638 faceoffs in 31 games, or about 51 per, including ~40 at EV and ~6 on each ST. Those numbers are significantly lower than the other teams in our little 10% sample, and it may be that it's a fundamental difference between the Devils and other teams, or simply between the Devils and these teams. More work required.

Nonetheless, this is sufficient to confirm my long time observation that 1 faceoff per minute is in the ballpark.

I'll look forward to it. Unfortunately, while NHL.com tracks which zone each faceoff is taken in and summarizes them in the reports for each game, those numbers don't seem to be on the season-to-date faceoff summary page ... they do home and road splits, and EV/PP/SH splits, but not OZ/DZ/NZ splits, at least not on that page. So it might take a bit of tinkering to get it all together.

Whats funny is that you have so much spare time to dedicate to proving that Marty is not the best Goalie of all time. You have compiles some impressive statistics, and compelling arguments. I am not going to spend time picking holes, because I don't think it needs to be done. What to me is not talked about, is how 1 goalie can play all those games for 1 team is impressive. He is part of the system, he is part of the reason for the low shot count. In fact for years they talked about him being a 3rd defense. The NHL changed the rules because of him to create more offense. No other goalie has had rule changes due to how they play.

As a goalie watcher, and a parent of a goalie, I show my child video of Tretiak, Roy, Hasek, and Brodeur. And talk to them about taking the best of what each do. In most conversations about goalies Vladislav is left out, but he is one of the greatest of all time. I have her watch for different reasons. And you can argue any way shape or form who was better. Brodeur is going to stand alone, as someone who played more games than anyone (Roy's body gave up, Hasek lost his job to Osgood in the playoffs cause he was ineffecitve)but Marty for every Bad game he has, the next game is usually incredible. If Detroit leaves Hasek in, Detroit gets eliminated. The Devils have tried to draft, find a goalie to replace him, but in the past 16 years they cannot find one. To me that is incredible. In NJ their fans are spoiled, and when he leaves, that team will find themselves a on the bottom for years.

About Me

I'm Philip Myrland, goalie stats blogger since 2007 and former writer for Hockey Prospectus. I call myself a contrarian because I rely mainly on stats-based analysis, think large sample sizes are more important than "big saves" and prefer to rank goalies based on save percentage rather than team success. In other words, pretty much the mainstream views of the hockey analytics community, but I've grown attached to the handle and plan to keep it as long as broadcasters everywhere keep bringing up GAA and wins. If you have any questions or comments contact me by email (contrariangoaltender@gmail.com). You can also follow me on Twitter (@tcghockey).